1. Field of the Invention
The present invention relates to an apparatus and method to convert an analog signal into a digital signal, and more particularly, to an apparatus and method to convert an analog signal into a digital signal, the apparatus and method performing a sampling operation by taking an average value of an analog signal for a predetermined sample period as a sample value and converting the analog signal into a digital signal using the sample value.
2. Description of the Related Art
A major reason for converting analog signals into digital signals is to effectively store, process, and reproduce images. In particular, with the development of digital technology, almost all information is converted from an analog form into a digital form and is processed accordingly.
To convert analog signals into digital signals, a sensor converting a signal to be measured into an analog signal and an analog/digital (A/D) converter converting the analog signal into a digital signal are required. The sensor converting the signal to be measured into the digital signal may be an image sensor, such as a camera, or a sound sensor such as a microphone. In addition, the sensor may be any sensor that can convert a signal to be measured into a digital signal, such as an optical sensor, a chemical sensor, a temperature sensor, and a pressure sensor.
FIG. 1 is a block diagram of a conventional apparatus 10 to convert an analog signal into a digital signal.
Referring to FIG. 1, the conventional apparatus 10 includes a sensor unit 11 to convert a signal to be measured into an analog signal, an amplification unit 12 to amplify the analog signal to an appropriate size, a sample/hold unit 13 to sample the analog signal at predetermined time intervals, and an analog/digital (A/D) converter 14 to convert the analog signal into a digital signal using a sample value.
A sampling process performed by the sample/hold unit 13 has a sample mode and a hold mode according to an operating mode of the sample/hold unit 13. In the sample mode, the sample/hold unit 13 has the same value as an analog signal input at a predetermined time. In the hold mode, the sample/hold unit 13 maintains a value immediately before the sample mode is changed to the hold mode. This sampling process is called a point sampling process. For example, referring to FIG. 2, the sample/hold unit 13 performs point sampling on an analog signal 21 input at time intervals using predetermined sampling frequencies. In FIG. 2, solid lines 22 indicate the analog signal 21 sampled using higher sampling frequencies than those used to sample the analog signal 21 indicated by dotted lines 23.
According to a Nyquist sampling theory, an input analog signal can be restored using a sampling frequency higher than a predetermined level. If a sampling frequency lower than the predetermined level is used, the input analog signal cannot be properly restored.
In the point sampling process described above, if an input analog signal is sampled at a peak point thereof, it can be properly restored. However, it is technically difficult to identify the peak point of each input analog signal. In other words, referring to FIG. 3, if a sample value 31a sampled from an input analog signal 31 is not the peak point of the input analog signal 31, when the input analog signal 31 is interpolated using the sample value 31a, there is a big difference between an interpolated analog signal 32 and the input analog signal 31.
In addition, a high sample frequency may be used to properly interpolate an input analog signal. However, as a higher sampling frequency is used, the amount of data is increased, which, in turn, increases memory required to store the data. Consequently, the time spent on transmitting data for information processing and communication is increased.
Therefore, a method of obtaining an interpolated signal close to an input analog signal without using an expensive high-performance sampling apparatus to identify the peak point of the input analog signal is required.
U.S. Pat. No. 5,117,227 discloses an apparatus to convert an input analog signal into an output digital signal using a method of counting a slope count and measuring a residual voltage to perform high-speed and high-precision continuous conversion. In this disclosure, the apparatus uses an integrator and a counter to convert a sampled/held signal into a digital signal. However, a method of obtaining an interpolated signal close to an input analog signal without using an expensive high-performance sampling apparatus to identify the peak point of the input analog signal is not suggested in this disclosure.